Electro mechanical brake tightening device

ABSTRACT

An electromechanical brake tightening device for a rail vehicle, includes a brake actuator to apply and release brakes. The actuator has a power converter to convert energy supplied by the brake actuator to a brake application movement. The power converter includes a shear force measuring bolt and/or a brake lever, arranged in a power transmission path of the converter to measure braking power.

[0001] The invention is based on an electromechanical brake tightening device, particularly for a rail vehicle brake, according to the type of claim 1.

[0002] Currently, three braking systems are essentially used in the rail vehicle sector: Electropneumatic braking systems, electrohydraulic braking systems as well as electromechanical braking systems. The braking system may be constructed as an active or passive braking system, depending on whether the force of a brake actuator has to be applied for braking (active braking system) or for releasing the brake (passive braking system). In the event of operating disturbances, an energy accumulation takes place in compressed-air reservoirs in the case of electropneumatic systems, in hydraulic reservoirs in the case of electrohydraulic systems and, and in the form of pre-loaded springs in the case of electromechanical systems.

[0003] From the prior art, electromechanical brake tightening devices for rail vehicles are known which have a brake actuator which comprises a service brake unit as well as an accumulator-type brake unit having an energy accumulator. The service brake unit contains a braking power generator for the application and/or release of the brake, for example, in the form of an electric motor drive. The accumulator-type brake unit comprises at least one energy accumulator for storing and supplying energy for the application of the brake as a service-type emergency brake in the sense of an underlying safety plane in the event of a failure of the service brake unit and/or as the parking brake. The accumulator-type brake unit is generally constructed as a spring-loaded brake.

[0004] A power converter provides a conversion of the energy supplied by the braking power generator and/or by the energy accumulator into a brake application movement. The electric-motor drive can be controlled by an electronic control and power system to carry out slip-controlled or load-corrected brakings. For the desired-actual comparison, values are required for the respectively present actual braking power, so that sensors for the direct braking power measurement or for measuring quantities from which the actual braking power can be derived have to be provided.

[0005] In the case of electropneumatic and electrohydraulic braking systems, pressure sensors are generally used for measuring the operating pressure existing in the compressed air or in the hydraulic liquid, from which operating pressure the amount of the momentary braking power can then be derived. However, such mediums do not exist in the case of electromechanical systems.

[0006] It is therefore an object of the present invention to provide an electromechanical brake tightening device of the initially mentioned type which permits a measuring of the braking power in a simple and precise manner.

[0007] According to the invention, this object is achieved by means of the characterizing features of claim 1.

ADVANTAGES OF THE INVENTION

[0008] The mechatronic shear force measuring bolt combines two functions by converting power and simultaneously measuring power. For this reason, the brake tightening device according to the invention, on the one hand, can have a small construction and, on the other hand, the number of component parts and the weight are reduced. The fact that the power sensor is directly integrated in the power flux of the power converter, in addition, results in a high measuring accuracy. For ensuring a reliable power transmission, the shear force measuring bolt can mechanically be designed to have a high fatigue strength.

[0009] As a result of the measures indicated in the subclaims, advantageous further developments and improvements of the brake tightening device indicated in claim 1 can be achieved.

[0010] According to a particularly preferable embodiment of the invention, the shear force measuring bolt forms a hinge bolt of a hinge mutually connecting at least two power transmission elements of the power converter. The hinge couples a connecting rod, which can be linearly operated by the brake actuator, to a brake lever of an eccentric arrangement acting upon brake shoes. As a result, the power measuring point is in the direct vicinity of the point of the power effect, which is why the influence of disturbance variables, such as the bearing friction or hysteresis, is low, permitting very precise measurements.

[0011] A preferred measure provides that the sensor for measuring the braking power contains at least one strain gauge held on the circumference of the shear force measuring bolt. It is known that strain gauges have a high measuring precision with a simultaneously broad measuring range and are insensitive to temperature changes and pressure surges, which is advantageous mainly in the case of the force effect occurring abruptly during emergency braking. Furthermore, they are distinguished by a good long-term stability as well as a high corrosion resistance.

[0012] According to a further development, redundant measuring sensors and/or redundant electronic sensor signal analyzing systems, particularly redundant measuring sensors with different measuring principles and/or redundant electronic sensor signal analyzing systems of different constructions and types are provided. As a result, an increased reliability of the measuring arrangement is achieved. In addition, a plausibility check can be carried out by comparing the measuring signals of two or more measuring circuits.

DRAWINGS

[0013] An embodiment of the invention is illustrated in the drawings and will be explained in detail in the following description.

[0014]FIG. 1 is a sectional view of a preferred embodiment of a brake actuator according to the invention which has an integrated shear force measuring bolt;

[0015]FIG. 2 is a sectional view of the shear force measuring bolt of FIG. 1 along Line II-II.

DESCRIPTION OF THE EMBODIMENT

[0016] The preferred embodiment of an electromechanical brake tightening device, which, as a whole, has the reference number 1 in FIG. 1, is provided for a rail vehicle and contains a brake actuator 2 having a service brake unit and an accumulator-type brake unit. The service brake unit has an electric drive, for example, an electric servo motor 4, which is accommodated in an actuator housing 6 of the brake actuator 2. A mechanical power converter 8 is used for converting the energy supplied by the brake actuator 2 to a brake application movement.

[0017] The servo motor 4 causes a coaxial brake spindle 10 to carry out rotations which are converted by means of the power converter to a brake application movement of brake pads 12 in the direction of a brake disk 14. The power converter 8 comprises, among other parts, a constructional spindle/nut unit 16 with a spindle nut 18 rotatably disposed on the brake spindle 10, which spindle nut 18 can carry out linear movements in the direction of the spindle axis when the brake spindle 10 is rotated. The end of the brake spindle 10 facing away from the servo motor 4 projects into a cylindrical hollow section of a connecting rod 20 which is connected in an axially fixed manner with the spindle nut 18. In addition, the cylindrical hollow section of the connecting rod 20 is held in an axially fixed manner in a sliding sleeve 22 against which at least one pre-loaded spring 24, which is supported on the actuator housing 6, is prestressed in the brake release position. The pre-loaded spring 24 is part of the accumulator-type brake unit and is used as an energy accumulator for storing and supplying energy for applying the brake as a service-type emergency brake in the sense of an underlying safety plane in the event of a failure of the service brake unit and/or as a parking brake. The service brake unit as well as the accumulator-type brake unit act upon the connecting rod 20. The pre-loaded spring 24 is held in the prestressed position by means of a locking device 26.

[0018] A plate-shaped connecting rod head 28 of the connecting rod 20 projects out of the sliding sleeve 22 and is provided with a connecting rod eye 30. As illustrated particularly in FIG. 2, a hinge bolt 32 extends through the connecting rod eye 30 as well as passage bores 34 coaxial thereto of cheeks 38 axially reaching around the connecting rod eye 30 and constructed at an end of a brake lever 36. The cheeks 38 of the brake lever 36, the connecting rod head 28 and the hinge bolt 32 together form a hinge of the power converter 8, whereby the brake lever 36 is linked perpendicularly to the spindle axis 42 to the connecting rod 20. When the brake spindle 10 is driven in the brake application direction or when the locking device 26 of the pre-loaded spring 24 is released, as a result of the then axially moving-out connecting rod 20, the hinge bolt 32 is stressed, among other things, by shear forces applied essentially perpendicular to the bolt axis 44.

[0019] The other end of the brake lever 36 acts upon an eccentric arrangement having an eccentric shaft 46 which is linked to a caliper lever 48 which, together with another caliper lever 50, forms a caliper 52. At one end of the calipers 48, 50, pad holders 54 are in each case arranged which have brake pads 12 displaceable in the direction of the axis of the brake disk 14. The ends of the caliper levers 48, 50 facing away from the brake pads 12 are connected with one another by way of a plunger rod adjuster 56 which is preferably designed to be electrically operated. The described arrangement also forms a part of the power converter 8 which converts the moving-out motion of the connecting rod 20 caused by the servo motor 4 or by the pre-loaded spring to a brake application movement of the brake pads 12 in the direction of the brake disk 14.

[0020] According to the invention, the hinge bolt 32 of the hinge 40 is formed by a shear force measuring bolt 58. The shear force measuring bolt is equipped with at least one measuring sensor 60 for measuring quantities from which the braking power acting at the brake pads 12 can be derived in an indirect or direct manner. In a preferred embodiment, the measuring sensor is formed by strain gauges (DMS) 60 which are accommodated, for example, in grooves 62 extending around in a plane perpendicular to the bolt axis 44. The grooves 62 with the strain gauges 60 are situated in the area of the axial junction points of the connecting rod head 28 with the cheeks 38 of the brake lever 36 and therefore precisely in the shearing planes of the shear force measuring bolt 58 stressed by shear. The strain gauges 60 are fastened to the circumference of the shear force measuring bolt 58 preferably by means of gluing in such a manner that they generate signals proportional to the shearing deformations of the shear force measuring bolt 58 caused by the shear forces acting in opposite directions, and supply these signals to an electronic analyzing system 64.

[0021] As an alternative, the grooves 62 may be eliminated and the strain gauges 60 may be fastened directly to the exterior surface of the shear force measuring bolt 58. According to another alternative or in addition, strain gauges 60 may be held in a hollow bore of the shear force measuring bolt 58 coaxial to the bolt axis 44, this shear force measuring bolt 58 then having a thin-walled construction. Instead of being fastened to the shear force measuring bolt 58, or in addition thereto, one or more strain gauges 60 may also be arranged on the brake lever 36, in order to be able to derive the braking powers from the deformations of the brake lever 36.

[0022] Furthermore, any other type of measuring sensor can be used by means of which the deformations of the shear force measuring bolt 58 and/or of the brake lever 36 occurring during the operation can be measured; thus, for example, pressure-measuring transducers which are integrated in the shear force measuring bolt 58 and which preferably operate according to a capacitive, a piezoelectric or a piezoresistive principle. In order to achieve a reliability of the measuring arrangement which is as high as possible, the measuring sensors 60 and/or the electronic analyzing system 64 may be provided in a redundant manner. In particular, redundant measuring sensors with different measuring principles and redundant electronic analyzing systems of a different construction and type may also be present.

[0023] The shear force measuring bolt 58 has an end-side bolt head 66 which has an enlarged diameter and in which an electronic sensor signal analyzing system 64 is accommodated; preferably in that it is cast into the bolt head 66, whereby a vibration-damping or vibration-uncoupling accommodation is provided. In the case of the preferably used strain gauges 60, the electronic analyzing system 64 contains a strain gauge bridge circuit. In the mounted condition, a face-side ring surface of the bolt head 66 impacts axially on the upper cheek 38 of the brake lever 36; the end of the shear force measuring bolt 58 pointing away from the bolt head 66 has two exterior grooves 68, which extend transversely with respect to the bolt axis 44, for receiving a position-securing snap ring.

[0024] A conversion of the shear deformation signals to signals for the respective actual braking power acting at the brake pads 12 also takes place in the electronic analyzing system 64, which signals are transmitted to a control and regulating device, which is not shown, in order to be able to set a desired braking power by means of a desired-actual comparison. Furthermore, the received signals for the actual braking power are used for monitoring the power input and the operability of the brake tightening device 1 during safety-relevant brakings. In addition, for verifying the measuring results, the motor current measured on the drive-side by a current sensor can be balanced with the signal for the actual braking power.

[0025] List of Reference Numbers 1 Brake tightening device 2 brake actuator 4 servo motor 6 actuator housing 8 power converter 10 brake spindle 12 brake pad 14 brake disk 16 spindle-nut constructional unit 18 spindle nut 20 connecting rod 22 sliding sleeve 24 pre-loaded spring 26 locking device 28 connecting rod head 30 connecting rod eye 32 hinge bolt 34 passage bores 36 brake lever 38 cheeks 40 hinge 42 spindle axis 44 bolt axis 46 eccentric shaft 48 caliper lever 50 caliper lever 52 caliper 54 pad holder 56 plunger rod adjuster 58 shear force measuring bolt 60 measuring sensor (strain gauge) 62 grooves 64 electronic analyzing system 66 bolt head 68 exterior grooves. 

1. Electromechanical brake tightening device (1), particularly for a rail vehicle brake, having a brake actuator (2) for the application and/or release of the brake, and having a power converter (8) for converting the energy supplied by the brake actuator (2) to a brake application movement, characterized in that the power converter (8) contains a shear force measuring bolt (58) and/or brake lever (36) arranged in the power flux and equipped with at least one measuring sensor for the indirect or direct braking force measurement.
 2. Electromechanical brake tightening device according to claim 1, characterized in that the shear force measuring bolt (58) forms a hinge bolt (32) of a hinge (40) mutually connecting at least two power transmission elements (20, 36) of the power converter (8).
 3. Electromechanical brake tightening device according to claim 2, characterized in that the hinge (40) connects a connecting rod (20) linearly operable by the brake actuator (2) with a brake lever (36) of an eccentric arrangement acting upon brake pads (12).
 4. Electromechanical brake tightening device according to claim 3, characterized in that the shear force measuring bolt (58) projects through a connecting rod head (28) of the connecting rod (20) as well as through passage bores (34) coaxial thereto of cheeks (38) of the brake lever (36) axially reaching around the connecting rod head (28).
 5. Electromechanical brake tightening device according to claim 4, characterized in that the brake lever (36) acts upon an eccentric arrangement having an eccentric shaft (46) which is linked to at least one caliper lever (48) which, together with another caliper lever (50), forms a caliper (52), pad holders with brake pads (12) being arranged at the ends of the caliper levers (48, 50), which brake pads (12) are displaceable in the direction of an axis of a brake disk (14).
 6. Electromechanical brake tightening device according to one of the preceding claims, characterized in that the measuring sensor for the indirect or direct braking power measurement contains at least one strain gauge (60) held on the circumference of the shear force measuring bolt (58) and/or on the circumference of the brake lever (36).
 7. Electromechanical brake tightening device according to one of the preceding claims, characterized in that the measuring sensor for the indirect or direct braking power measurement contains at least one strain gauge (60) held in a hollow bore of a thin-walled shear force measuring bolt.
 8. Electromechanical brake tightening device according to one of the preceding claims, characterized in that recesses (62) for accommodating the strain gauges (60) are provided on the circumference of the shear force measuring bolt (58), which recesses (62) are situated in the area of axial junction planes of the connecting rod head (28) with the cheeks (38) of the brake lever (36).
 9. Electromechanical brake tightening device according to one of the preceding claims, characterized in that the measuring sensor (60) for the indirect or direct braking power measurement contains at least one pressure-measuring transducer integrated in the shear force measuring bolt (58), preferably a pressure-measuring transducer operating according to a capacitive, piezoelectric or piezoresistive principle.
 10. Electromechanical brake tightening device according to one of the preceding claims, characterized in that the shear force measuring bolt (58) has an end-side bolt head (66) which has an enlarged diameter and in which an electronic sensor signal analyzing system (64) is arranged.
 11. Electromechanical brake tightening device according to claim 10, characterized in that the electronic sensor signal analyzing system (64) is cast into the bolt head (66) in a shake-proof and shock-proof manner.
 12. Electromechanical brake tightening device according to claim 11, characterized in that redundant measuring sensors (60) and/or redundant electronic sensor signal analyzing systems (64), particularly redundant measuring sensors with different measuring principles and/or redundant electronic sensor signal analyzing systems of a different construction and type are provided.
 13. Electromechanical brake tightening device according to one of the preceding claims, characterized in that, by means of the measuring sensor (60), actual values for the momentary braking power can be supplied as signals to a regulating device.
 14. Electromechanical brake tightening device according to one of the preceding claims, characterized in that the brake actuator (2) contains an electric motor (4) whose motor current can be detected by a current sensor.
 15. Electromechanical brake tightening device according to claim 14, characterized in that the signal for the motor current can be balanced with the signal for the braking power. 